Detailed Description of the Invention
1. Technical Field of the Invention
The present invention relates to a driving device for a brushless motor that is having a polyphase structure, and more particularly to a driving device for a polyphase motor excellent in temperature characteristic and capable of simplifying the circuit structure through the use of a magnetoresistance effect element for a rotation detector.
2. Prior Art
FIG. 14 is a structural view showing a driving device for a three-phase brushless motor as an example of a conventional driving device for a polyphase motor, and FIG. 15 is a timing chart for the Hall signal and phase current in FIG. 14.
In FIG. 14, a reference numeral 1 designates a brushless three-phase motor consisting of driving coils 1U (U-phase), 1V (V-phase) and 1W (W-phase).
In this three-phase motor 1, a rotor is rotatably supported on a stator, which is located on the fixed portion side. The stator is provided with the driving coils 1U, 1V and 1W, and in positions adjacent these coils, with hole elements H1, H2 and H3 respectively. On the inner surface of a rotor case (not shown), there are provided ring-shaped rotor magnets, in which N-poles and S-poles are alternately arranged, and the Hall elements H1, H2 and H3 are provided in positions opposed to these rotor magnets respectively. When the rotor rotates, each magnetic pole of the rotor magnet passes the Hall elements H1, H2 and H3 respectively, and at this time, the Hall elements H1, H2 and H3 detect changes in the magnetic field.
Output signals from the Hall elements H1, H2 and H3 are inputted into driving means 2. As shown in FIG. 14, the driving means 2 comprises voltage follower means 3, control means 4 and phase current generating means 5.
By receiving the output signals from the Hall elements H1, H2 and H3 by a high-input impedance element consisting of an operational amplifier and the like, the voltage follower means 3 plays a part of accurately transmitting the output signals of the Hall signals to the control means 4 in the next stage. Also, within the control means 4, there is provided amplification means (not shown) to amplify the output signals from the Hall elements H1, H2 and H3 having a low signal level into such hole signals Hu, Hv and Hw which are prone to be signal-processed as shown in FIG. 15.
Also, the control means 4 generates driving signals 4u, 4v and 4w for which timing adjustment has been performed on the basis of each Hall signal Hu, Hv and Hw. Thus, in the phase current generating means 5, driving signals 4u, 4v and 4w are voltage-current converted into phase current Iu, Iv and Iw respectively. At this time, each phase current Iu, Iv and Iw is converted in line with the timing of the driving signals 4u, 4v and 4w respectively, and is supplied to each driving coil 1U, 1V and 1W of the three-phase motor 1.
In this manner, the construction of three-phase motor 1 makes it possible to always maintain the rotational speed and rotational phase of the rotor with high accuracy by performing feedback control in which the rotational speed and rotational phase of the rotor are detected to supply optimum phase current Iu, Iv and Iw to the driving coils 1U, 1V and 1W for each phase in real time.